Electrowetting display device including a strengthened hydrophobic layer

ABSTRACT

An electrowetting display device includes a base substrate, a hydrophobic layer disposed on the base substrate and including at least about 49 atomic percent (at %) of fluorine atoms in a surface thereof, a wall disposed on the base substrate which partitions a pixel area, and an electrowetting layer that includes a first fluid and a second fluid, which are disposed in the pixel area and are immiscible with each other. The second fluid has an electrical conductivity or a polarity. The electrowetting display device further includes an electronic device is configured to apply an electric field to the electrowetting layer to control the electrowetting layer.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of, and claims priority to, U.S. patentapplication Ser. No. 13/688,810, filed on Nov. 29, 2012, entitled“Electrowetting Display Device Including a Strengthened HydrophobicLayer”, which claims priority under 35 U.S.C. §119 to Korean PatentApplication No. 10-2012-0028374, filed on Mar. 20, 2012, the disclosureof which are hereby incorporated by reference herein in their entirety.

TECHNICAL FIELD

The present disclosure relates to an electrowetting display device usingan electrowetting effect and a method of manufacturing theelectrowetting display device.

DISCUSSION OF THE RELATED ART

Various display devices, such as, for example, a liquid crystal display(LCD), a plasma display panel (PDP), an organic light emitting display(OLED), a field effect display (FED), an electrophoresis display (EPD),an electrowetting display (EWD), etc., are being used as flat paneldisplay devices.

Among these display devices, the electrowetting display may beconfigured to apply a voltage to an aqueous liquid electrolyte to changea surface tension of the aqueous liquid electrolyte, and thus theelectrowetting display may reflect or transmit light from the outside,thereby displaying desired images.

SUMMARY

Exemplary embodiments of the present invention provide an electrowettingdisplay device having increased display quality.

Exemplary embodiments of the present invention provide a method ofmanufacturing an electrowetting display device having increased displayquality.

Exemplary embodiments of the present invention provide an electrowettingdisplay device which includes a base substrate, a hydrophobic layerdisposed on the base substrate and including at least about 49at % offluorine atoms in a surface thereof, a wall disposed on the basesubstrate which partitions a pixel area, an electrowetting layer thatincludes a first fluid and a second fluid, which are disposed in thepixel area and are immiscible with each other. The second fluid has anelectrical conductivity or a polarity. The electrowetting display devicefurther includes an electronic device configured to apply an electricfield to the electrowetting layer to control the electrowetting layer.

The hydrophobic layer includes an amorphous fluorine compound includingat least one of -CxFy-, CxFyHz-, -CxFyCzHp-, -CxFyO—, or -CxFyN(H)—,where each of x, y, x, p is an integer number which is no less than 1.The hydrophobic layer includes a planarization portion substantiallyparallel to an upper surface of the base substrate and an edge portiondisposed at side portions of the planarization portion and inclined withrespect to the wall.

The wall is disposed on the hydrophobic layer, or the hydrophobic layeris provided in the pixel area.

Exemplary embodiments of the present invention provide an electrowettingdisplay device which includes a base substrate, a hydrophobic layerdisposed on the base substrate, a wall disposed on the base substratewhich partitions a pixel area, and an electrowetting layer that includesa first fluid and a second fluid, which are disposed in the pixel areaand are immiscible with each other. The second fluid has an electricalconductivity or a polarity. The electrowetting display device furtherincludes an electronic device disposed on the base substrate which isconfigured to control the electrowetting layer.

The hydrophobic layer includes a planarization portion substantiallyparallel to an upper surface of the base substrate and an edge portiondisposed at side portions of the planarization portion and inclined withrespect to the wall.

Exemplary embodiments of the present invention provide a method ofmanufacturing an electrowetting display device. The method includesforming a hydrophobic layer on a base substrate, forming a wall on thebase substrate to partition a pixel area, reflowing the hydrophobiclayer at a temperature higher than a glass transition temperature of thehydrophobic layer to form a second hydrophobic layer, forming anelectrowetting layer in the pixel area, and forming an electronic devicethat controls the electrowetting layer.

The hydrophobic layer is plasma-treated before the wall is formed.

Exemplary embodiments of the present invention provide an electrowettingdisplay device which includes a base substrate, a hydrophobic layerdisposed on the base substrate, a wall disposed on the base substratewhich partitions a pixel area, an electrowetting layer which includes afirst fluid and a second fluid. The first fluid and the second fluid aredisposed in the pixel area and are immiscible with each other, and thesecond fluid has an electrical conductivity or a polarity. Theelectrowetting display device further includes an electronic devicedisposed on the base substrate and on a lower surface of theelectrowetting layer is configured to control the electrowetting layer.In addition, the electrowetting display device further includes aninsulating layer covering the electronic device.

The hydrophobic layer includes a planarization portion substantiallyparallel to an upper surface of the base substrate and an edge portiondisposed at side portions of the planarization portion and inclined withrespect to the wall. The edge portion of the hydrophobic layer makesdirect contact with the wall and a contact angle between the hydrophobiclayer and the wall is smaller than a right angle. Moreover, a height ofan end portion of the edge portion of the hydrophobic layer is lowerthan a height of the wall.

According to the above, the display quality of the electrowettingdisplay device may be increased. The non-closing defective of theelectrowetting display device may be reduced, so that the electrowettingdisplay device may readily display black gray scale.

BRIEF DESCRIPTION OF THE FIGURES

Exemplary embodiments of the present invention can be understood in moredetail from the following detailed description when taken in conjunctionwith the accompanying drawings wherein:

FIG. 1 is a cross-sectional view showing a portion of an electrowettingdisplay device according to an exemplary embodiment of the presentinvention;

FIG. 2 is circuit diagram showing a switching device in an active matrixpixel circuit;

FIG. 3 is a flowchart showing a method of manufacturing theelectrowetting display device shown in FIG. 1 according to an exemplaryembodiment of the present invention;

FIGS. 4A to 4F are cross-sectional views showing a method ofmanufacturing the electrowetting display device shown in FIG. 1according to an exemplary embodiment of the present invention;

FIGS. 5A to 5D are SEM images showing a hydrophobic layer and a wall;

FIG. 6 is a plan view showing the electrowetting display device shown inFIG. 1 according to an exemplary embodiment of the present invention;

FIG. 7 is a cross-sectional view taken along a line I-I shown in FIG. 6;

FIG. 8 is a cross-sectional view showing a portion of an electrowettingdisplay device according to an exemplary embodiment of the presentinvention;

FIG. 9 is a flowchart showing a method of manufacturing anelectrowetting display device shown in FIG. 8 according to an exemplaryembodiment of the present invention;

FIGS. 10A to 10F are cross-sectional views showing a method ofmanufacturing the electrowetting display device shown in FIG. 1according to an exemplary embodiment of the present invention; and

FIG. 11 is a cross-sectional view showing an electrowetting displaydevice according to an exemplary embodiment of the present invention.

DETAILED DESCRIPTION

It will be understood that when an element or layer is referred to asbeing “on”, “connected to” or “coupled to” another element or layer, itcan be directly on, connected or coupled to the other element or layeror intervening elements or layers may be present. Like numbers refer tolike elements throughout. As used herein, the term “and/or” includes anyand all combinations of one or more of the associated listed items. Inthe drawings, the thickness of layers, films, panels, regions, etc., maybe exaggerated for clarity.

As used herein, the singular forms, “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise.

Hereinafter, an exemplary embodiment of the present invention will beexplained in detail with reference to the accompanying drawings.

FIG. 1 is a cross-sectional view showing a portion of an electrowettingdisplay device according to an exemplary embodiment of the presentinvention. The electrowetting display device includes a plurality ofpixels PXL, and one of the pixels PXL has been shown in FIG. 1. In FIG.1, a range of the pixel PXL has been represented by two dotted lines.

Referring to FIG. 1, each pixel PXL includes, for example, a first basesubstrate BS1, a second base substrate BS2, a wall WL, a hydrophobiclayer HPL, and an electrowetting layer EWL.

The electrowetting display device includes a front surface on which animage is displayed and a rear surface opposite to the front surface. Aviewer may perceive the image displayed on the electrowetting displaydevice in front of the front surface. In the present exemplaryembodiment, an outer surface of the second base substrate BS2 (e.g., anupper surface of the second base substrate BS2 in FIG. 1) is referred toas the front surface or the upper surface and an opposite surface to thefront or upper surface is referred to as the rear surface or a lowersurface. However, exemplary embodiments of the present invention are notlimited to the above-mentioned position of the front surface and therear surface. That is, the position of the front and rear surfaces maybe changed depending on an operation mode of the electrowetting displaydevice, such as, for example, a reflective mode, a transmissive mode, atransflective mode, etc. The electrowetting display device may be, forexample, a segmented display type in which the image is built up ofsegments. The electrowetting display device may be, for example, anactive matrix driving display device or a passive matrix driving displaydevice.

Each of the first base substrate BS1 and the second base substrate BS2is formed in an inseparable single body to be commonly shared by thepixels PXL or formed in plural numbers to be used as a portion of eachpixel PXL. The first base substrate BS1 and/or the second base substrateBS2 may be, but are not limited to, a transparent insulator or apolymer, such as glass, plastic, etc. When the first base substrate BS1and/or the second base substrate BS2 is a plastic substrate, the firstbase substrate BS1 and/or the second base substrate BS2 may be formedof, for example, polyethylene terephthalate (PET), fiber reinforcedplastic (FRP), or polyethylene naphthalate (PEN). In addition, the firstbase substrate BS1 and/or the second base substrate BS2 may be rigid orflexible.

The wall WL is disposed on the first base substrate BS1 to define aspace surrounded by the first base substrate BS1 and the wall WL. Thespace may be, for example, a pixel area PA corresponding to each pixelPXL. Accordingly, the area of the pixel area PA may be limited by thewall WL, and the area of the pixel area PA has been represented bydotted lines. In the present exemplary embodiment, the wall WL is formedon the first base substrate BS1 and the first base substrate BS1 and thewall WL define the pixel area PA, but exemplary embodiments are notlimited thereto or thereby. For instance, the pixel area PA may bedefined by the first base substrate BS1, the second base substrate BS2,and the wall WL.

The first and second electrowetting layers EWL1 and EWL2 are provided inthe pixel area PA. The first electrowetting layer EWL1 may include, forexample, a first fluid FL1 and the second electrowetting layer EWL2 mayinclude, for example, a second fluid FL2. The first and second fluidsFL1 and FL2 are immiscible with each other. The second fluid FL2 has,for example, an electrical conductivity or a polarity. For example, inan embodiment, the second fluid FL2 may be a polar liquid aqueoussolution (Aq) such as water or a salt solution such as a solution ofsodium chloride or potassium chloride in water. In the present exemplaryembodiment, the second fluid FL2 includes, for example, potassiumchloride or sodium chloride solution (Aq) dissolved in a mixture ofwater and ethyl alcohol. The second fluid FL2 may be transparent or havea color. As an example, the second fluid FL2 may have a white color toabsorb or reflect light from the outside. The first fluid FL1 has, forexample, a non-electrical conductivity. For example, in an embodiment,the first fluid FL1 may include an alkane like hexadecane, decane,dodecane, tetradecane, or an oil like silicone oil.

The first fluid FL1 may absorb at least a portion of the opticalspectrum. The first fluid FL1 may transmit a portion of the opticalspectrum, so the first fluid FL1 displays a color. The first fluid FL1may include, for example, pigments or dyes to display the color.According to an exemplary embodiment, the first fluid FL1 may be tingedwith, for example, black. In this case, the first fluid FL1 may absorbsubstantially the entire optical spectrum of visible light. In addition,the second fluid FL2 may reflect the optical spectrum.

Alternatively, in an embodiment the first fluid FL may include othercolor dyes or pigments other than a black color, so that the displayapparatus may display various colored images. For example, in anembodiment, the first fluid FL may include other dyes or pigments ofprimary colors such as red, green, cyan, magenta, blue, or yellow.

The hydrophobic layer HPL is disposed on the first base substrate BS1.In the present exemplary embodiment, as the wall WL is disposed on thehydrophobic layer HPL, the hydrophobic layer HPL is disposed between thefirst base substrate BS1 and the wall WL when viewed in across-sectional view. The hydrophobic layer HPL may be formed, forexample, in a single body to cover the pixels PXL. Meanwhile, aninsulating layer INS is disposed between the first base substrate BS1and the hydrophobic layer HPL, and the insulating layer INS may have,for example, a multi-layer structure, e.g., a double-layer structure, ormay be omitted.

The hydrophobic layer HPL may have, for example, permeability orreflexibility. When the hydrophobic layer HPL has reflexibility, lightfrom the outside may be reflected by the hydrophobic layer HPL. Inaddition, the hydrophobic layer HPL may have, for example, a white coloror reflect a portion of the light corresponding to a specific wavelengthto have a specific color. The hydrophobic layer HPL includes, forexample, a material having hydrophobicity, e.g., a compound of fluorineatoms. The material of the hydrophobic layer HPL is formed of compoundwhich contains, for example, about 49 atomic percent (at %) of fluorineatoms or more in its surface to allow the surface to have thehydrophobicity. The compound of the hydrophobic layer HPL may be, forexample, a polymer compound represented by the following chemicalformulas, such as -CxFy-, CxFyHz-, -CxFyCzHp-, -CxFyO—, -CxFyN(H)—,etc., where each of x, y, x, p is an integer number equal to or largerthan I), or an amorphous fluorine compound, such as, for example,copolymers of tetrafluoroethylene (TFE) and perfluro-2,2 dimethyl 1, 3dioxide (PDD), sold under the brand name TEFLON® AF 1600 which is aregistered trademark of the E.I. DuPont de Nemours and CompanyCorporation, 101 West 10th St., Wilmington, Del. 19898). Alternatively,other low surface energy polymers such as, for example, parylene may beused to form the hydrophobic layer HPL. In the present exemplaryembodiment, the term of “surface of the hydrophobic layer HPL” is usedto define a thin layer having, for example, a thickness of about 50angstroms to about 100 angstroms from the upper surface of thehydrophobic layer HPL to the lower surface of the hydrophobic layer HPL.

The first fluid FLI should have a hydrophobicity sufficient to beattached to the hydrophobic layer HPL when compared with the secondfluid FL2. The hydrophobic layer HPL contains, for example, about 49at %of fluorine atoms in the surface thereof, and thus the first fluid FL1has wettability higher than that of the second fluid FL2 with respect tothe surface of the hydrophobic layer HPL. The wettability indicates arelative affinity of fluid against a surface of a solid. For example, inthe present exemplary embodiment, a contact angle of water with respectto the hydrophobic layer HPL is about 10 W or more, and the hydrophobiclayer HPL has a surface tension of about 16 dyne/cm or more.

The hydrophobic layer HPL includes, for example, a planarization portionPLP substantially parallel to the upper surface of the first basesubstrate BS1 and an edge portion EDG disposed at side portions of theplanatization portion PLP and inclined with respect to the wall WL. Theedge portion EDG is disposed adjacent to the wall WL and directly makescontact with the wall WL. The contact angle between the hydrophobiclayer HPL and the wall WL is, for example, smaller than a right angle.An end portion of the edge portion EDG of the hydrophobic layer HPL ispositioned, for example, at a height higher than an end portion of theplanarization portion PLP when viewed in a cross-sectional view. In thepresent exemplary embodiment, the term of “height” is used, for example,to indicate a distance from an upper surface of a lower layer disposedunder a specific layer. The height of the end portion of the edgeportion EDG is, for example, lower than that of the wall WL and largerthan about 1/100 of the height of the wall WL. In addition, the heightof the end portion of the edge portion EDG is, for example, smaller thanabout 99/100 of the height of the wall WL.

Each pixel PXL includes, for example, an electronic device that appliesan electric field to the first and second electrowetting layers EWL1 andEWL2 to control the first and second electrowetting layers EWL1 andEWL2. The electronic device includes, for example, a first electrode EL1disposed on the first base substrate BS1, a switching device (not shown)connected to the first electrode EL1, and a second electrode EL2disposed on the second base substrate BS2. The first electrode EL1 isdisposed between the first base substrate BS1 and the hydrophobic layerHPL, and an insulating layer INS is disposed between the first basesubstrate BS1 and the first electrode EL1.

The first electrode EL1 is separated from the first and secondelectrowetting layers EWL1 and EWL2 by the hydrophobic layer HPL. Thefirst electrode EL1 may be provided in a desired shape. The firstelectrode EL1 is applied with a voltage signal by the switching device.The second electrode EL2 may be formed, for example, in a single body tocover all the pixels PXL. Although not shown in figures, in the casethat the second electrode EL2 is divided into a plurality of secondelectrodes EL2, which respectively correspond to the pixels PXL, thesecond electrodes EL2 may be electrically connected to each other by thesecond fluid FL2.

In the present exemplary embodiment, the first electrode EL1 and thesecond electrode EL2 are respectively disposed on the first basesubstrate BS1 and the second base substrate BS2, but exemplaryembodiments of the present invention are not limited thereto or thereby.For instance, all the first and second electrodes EL1 and EL2 may bedisposed on the first base substrate BS1. In this case, the secondelectrode EL2 may be provided on at least one side portion of the firstelectrode EL1 and electrically insulated from the first electrode EL1.

The pixel PXL is controlled by a voltage or potential difference appliedbetween the first electrode EL1 and the second electrode EL2. The firstelectrode EL1 disposed on the first base substrate BS1 is connected tothe switching device.

The movement of the first fluid FL1 may be limited in each pixel PXL bythe wall WL of the pixel PXL. The wall WL may have hydrophilicity topush out the first fluid FL1. In the present exemplary embodiment, thewall WL extends in, for example, a direction from the first basesubstrate BS1 to the second base substrate BS2. However, exemplaryembodiments of the present invention are not limited to the aboveposition for the wall WL. For example, alternatively, in an embodiment,the wall WL may extend in a direction from the second base substrate BS2to the first base substrate BS1.

The pixel PXL may be in an ON-state when the voltage difference, whichis not zero, is applied to the first electrode FL1 and the secondelectrode FL2. An electrostatic force caused by the voltage differencemay move the second fluid FL2 to the first electrode EL1, and thus thefirst fluid FL1 may be pushed out from at least a portion of thehydrophobic layer HPL to the wall WL surrounding the hydrophobic layerHPL. When the first fluid FL1 is completely pushed out, the first fluidFL1 may have a drop shape as shown by the dotted line. Accordingly, thehydrophobic layer HPL of the pixel PXL is exposed through the firstfluid FL1. When the voltage applied to the pixel PXL returns to aboutzero volts, the pixel PXL may return to an OFF-state, so the first fluidFL1 covers the hydrophobic layer HPL again. The first fluid FL1 may thusserve as an optical switch that is able to be electrically controlled ineach pixel PXL.

FIG. 2 is circuit diagram showing a switching device in an active matrixpixel circuit. In the present exemplary embodiment, each pixel mayinclude one or more transistors, but FIG. 2 shows that each pixelincludes a corresponding one transistor.

The switching device includes, for example, a transistor TR, first andsecond capacitors CP1 and CP2, and connection lines GL and DL.

The transistor TR includes, for example, a gate electrode, a sourceelectrode, and a drain electrode. The connection lines include, forexample, a gate line GL and a data line DL, which are connected to thetransistor TR. The gate electrode is connected to the gate line GL, thesource electrode is connected to the data line DL, and the drainelectrode is connected to the first and second capacitors CP1 and CP2.The first capacitor CP1 is, for example, an electrowetting capacitorconfigured to include a first electrode, a second electrode, and a fluidprovided between the first electrode and the second electrode. Thesecond electrode is connected to a common voltage Vcom applied to asecond fluid making contact with the second electrode. The secondcapacitor CP2 is, for example, a storage capacitor configured to includethe drain electrode (and/or first electrode), a storage electrode STE,and an insulating layer disposed between the two electrodes. The storageelectrode STE is connected to a storage line STL.

The voltage applied to the first electrode is set by the data line DLwhile the switching device is operated. When a gate signal is applied tothe gate line GL, the transistor is turned on, and thus the voltageapplied to the data line DL is applied to the first and secondcapacitors CP1 and CP2. After the data voltage is applied to the firstelectrode, the data voltage remains in the capacitors due to a couplingcapacitance of the first and second capacitors CP1 and CP2 so as todrive the pixel until the voltage is refreshed.

FIG. 3 is a flowchart showing a method of manufacturing theelectrowetting display device shown in FIG. 1 according to an exemplaryembodiment of the present invention. FIGS. 4A to 4F are cross-sectionalviews showing a method of manufacturing the electrowetting displaydevice shown in FIG. 1 according to an exemplary embodiment of thepresent invention.

Referring to FIG. 3, the electrowetting display device of FIG. 1 ismanufactured by forming the electronic device on the base substrate,forming the hydrophobic layer HPL on at least a portion of the basesubstrate, plasma-treating the hydrophobic layer HPL, forming the wallWL on the hydrophobic layer HPL, reflowing the hydrophobic layer HPL,and forming the first electrowetting layer EWL1 and the secondelectrowetting layer EWL2.

Hereinafter, the method of manufacturing the electrowetting displaydevice of FIG. 1 will be described in detail with reference to FIGS. 1,3 and 4A to 4F.

Referring to FIGS. 3 and 4A, the base substrate is prepared and theelectronic device is formed on the base substrate (S110).

The base substrate includes, for example, the first base substrate BS1and the second base substrate BS2. The electronic device includes, forexample, the first electrode EL1, the second electrode EL2, and theswitching device. In FIG. 4A, the first electrode EL1 is formed on thefirst base substrate BS1. In FIG. 4A, the second base substrate BS2, thesecond electrode EL2, and the switching device are omitted.

The insulating layer INS is formed on the first base substrate BS1 onwhich the first electrode EL1 is formed, and thus the first electrodeEL1 is covered by the insulating layer INS.

Referring to FIGS. 3 and 4B, the hydrophobic layer HPL is formed on thefirst base substrate BS1 (S120). The hydrophobic layer HPL is formed byusing, for example, a compound containing fluorine atoms. The compoundmay be, for example, a polymer compound represented by the followingchemical formulas, such as -CxFy-, CxFyHz-, -CxFyCzHp-, -CxFyO—,-CxFyN(H)—, etc., (where each of x, y, x, p is an integer number equalto or larger than 1), or the amorphous fluorine compound represented bythe following chemical formula 1, such as, for example, copolymers oftetrafluoroethylene (TFE) and perfluro-2,2 dimethyl 1, 3 dioxide (PDD),sold under the brand name TEFLON® AF 1600 which is a registeredtrademark of the E.I. DuPont de Nemours and Company Corporation, 101West 10th St., Wilmington, Del. 19898). Alternatively, other low surfaceenergy polymers such as, for example, parylene may be used to form thehydrophobic layer HPL. In the chemical formula 1, m and n is a naturalnumber.

Then, although not shown in figures, the hydrophobic layer HPL ispatterned. The patterning is performed, for example, to expose a portionof the electronic device, e.g., a portion of the connection line, andthus external lines may be connected to the electronic device.

For example, referring to FIGS. 3 and 4C, a plasma treatment isperformed on the hydrophobic layer HPL (S130). The plasma treatment isperformed to allow the surface of the hydrophobic layer HPL havinghydrophobicity to temporarily have hydrophilicity. In the case that thehydrophobic layer HPL maintains its hydrophobicity, an adhesive propertybetween the hydrophobic layer HPL and the wall WL may be poor.Accordingly, when the surface of the hydrophobic layer HPL isplasma-treated to have the hydrophilicity as shown in FIG. 4C, theadhesive property between the wall WL and the hydrophobic layer HPL maybe increased.

Referring to FIGS. 3 and 4D, the wall WL is formed on the plasma-treatedhydrophobic layer HPL (S140). The wall WL may be formed of, for example,a photosensitive organic material, such as a photoresist, or a heatcurable organic material. The wall WL, for example, may include an epoxycompound represented by the following chemical formula 2.

In the case that the wall WL is formed of the photosensitive organicmaterial, the wall WL may be formed by, for example, a photolithographyprocess including exposure and development processes. For example, thephotosensitive organic material is patterned through thephotolithography process and cured through a baking process, therebyforming the wall WL with the photosensitive organic material. Thehydrophilic portion of the hydrophobic layer HPL may be removed by, forexample, the development process of the photolithography process, butexemplary embodiments of the present invention are not limited to thedevelopment process. That is, the hydrophilic portion of the hydrophobiclayer HPL may be removed separately using, for example, a washingsolution or an etchant.

Referring to FIGS. 3 and 4E, after the wall WL is formed, thehydrophobic layer HPL is, for example, reflowed (S150). Residues andhydrophilic functional groups (e.g., —OH, —CHO, —COOH, etc.) on thehydrophobic layer HPL are removed or relocated into the inside of thehydrophobic layer HPL through the reflowing process, so that thehydrophobicity on the surface of the hydrophobic layer HPL may beincreased. The residues and hydrophilic functional groups are generatedin the plasma treatment process and the process of forming the wall WL.The reflow process is performed, for example, by heating the hydrophobiclayer HPL at a temperature higher than a glass transition temperature Tgof the material for the hydrophobic layer HPL. The reflow temperature ofthe hydrophobic layer HPL is in a range of, for example, about 160° C.to about 280° C. When the hydrophobic layer HPL is formed of the organicmaterial represented by the chemical formula I, the reflow process isperformed at the reflow temperature of, for example, about 160° C. ormore. For example, the reflow process may be performed at the reflowtemperature of about 220° C. for about one hour. In the reflow process,the atoms in the hydrophobic layer HPL may be rearranged so as to allowan interfacial energy between the hydrophobic layer HPL and air to beminimized. Thus, the hydrophilic functional groups may enter inside thehydrophobic layer HPL and hydrophobic functional groups, e.g., fluorine(F), may come up to the surface. As a result, the hydrophobicity of thehydrophobic layer HPL may be strengthened again.

In the reflow process, a creep phenomenon, in which the surface of theedge portion EDG slides upward along the wall WL as it is closer to thewall WL, may occur when the reflow temperature is equal to or higherthan the glass transition temperature and a surface tension differencebetween the hydrophobic layer HPL and the wall WL is equal to or higherthan gravity. In this case, the height of the end portion of the edgeportion EDG may be varied depending on, for example, the temperature,the process time, and the surface tension of the wall WL and thehydrophobic layer HPL of the reflow process. For example, when thehydrophobic layer HPL is represented by the chemical formula 1, thesurface tension of the hydrophobic layer HPL is about 17 dyne/cm, andwhen the wall WL is represented by the chemical formula 2, the surfacetension of the wall WL is about 45 dyne/cm.

FIGS. 5A to 5D are SEM images showing the hydrophobic layer HPL and thewall WL. For example, FIG. 5A shows the hydrophobic layer HPL and thewall WL before the reflow process is performed on the hydrophobic layerHPL and the wall WL, FIG. 5B shows the hydrophobic layer HPL and thewall WL after the reflow process is performed on the hydrophobic layerHPL and the wall WL at the temperature of about 220 degrees, FIG. 5Cshows the hydrophobic layer HPL and the wall WL after the reflow processis performed on the hydrophobic layer HPL and the wall WL at thetemperature of about 240 degrees, and FIG. 5D shows the hydrophobiclayer HPL and the wall WL after the reflow process is performed on thehydrophobic layer HPL and the wall WL at the temperature of about 260degrees. As shown in FIGS. 5A to 5D, the creep phenomenon of the edgeportion EDG of the hydrophobic layer HPL may occur when the reflowprocess is performed on the hydrophobic layer HPL and the wall WL.

Referring to FIGS. 3 and 4F, the first and second electrowetting layersEWL1 and EWL2 are formed between the first base substrate BS1 and thesecond base substrate BS2 (S160). The first electrowetting layer EWL1may include, for example, the first fluid FL1 and the secondelectrowetting layer EWL2 may include, for example, the second fluidFL2. In the present exemplary embodiment, the first fluid FL1 is formedin the display area defined by the wall WL.

The electrowetting display device manufactured by the above-mentionedmethod may reduce a non-closing defective when the electrowettingdisplay device is operated.

The non-closing defective indicates that the first fluid FL1 does notcompletely cover the hydrophobic layer HPL when the voltage is appliedto or not applied to each pixel and a black state is improperlyrepresented. The non-closing defective may be caused by the residuesgenerated during the processes performed after the hydrophobic layer HPLis formed or the hydrophilic functional groups not removed from thehydrophobic layer HPL. For example, the non-closing defective may becaused by hydrophilic functional groups generated by a reaction betweenthe hydrophilic functional groups generated during the plasma treatmenton the hydrophobic layer HPL and functional groups of a material for thewall. For instance, when the hydrophobic layer HPL represented by thechemical formula 1 is plasma-treated, —OH group or —COOH group may beadsorbed onto a tip of the polymer and —OH group or —COOH group mayreact with an epoxy group of the wall represented by the chemicalformula 2, thereby causing other hydrophilic functional groups.

According to the present exemplary embodiment, the hydrophobicity of thehydrophobic layer HPL may be strengthened by reflowing the hydrophobiclayer HPL to which the hydrophilic functional groups are adsorbed. Thatis, during the reflow process, the atoms in the hydrophobic layer HPLmay be rearranged so as to allow the interfacial energy between thehydrophobic layer HPL and air to be minimized. Thus, the hydrophilicfunctional groups may enter inside the hydrophobic layer HPL andhydrophobic functional groups, e.g., fluorine (F), may come up to thesurface of the hydrophobic layer HPL. As a result, the hydrophobicity ofthe hydrophobic layer HPL may be strengthened and the non-closingdefective may be reduced.

Table 1 shown below illustrates the atom content in the hydrophobiclayer HPL before and after performing the reflow process when thehydrophobic layer HPL and the wall are formed. In Examples 1 to 5,exposure and baking conditions are partially changed, but thehydrophobic layer HPL and the wall WL are formed under the sameexperimental conditions.

TABLE 1 Atom content before Atom content after reflow process reflowprocess Example C O F C O F 1 47.98 13.07 38.95 36.42 11.74 51.83 245.79 13.14 41.07 35.59 11.74 52.66 3 47.23 11.71 41.05 35.96 11.5152.53 4 50.23 14.47 35.30 36.95 11.44 51.61 5 49.61 13.5 I 36.88 37.2611.44 51.30 8 45.84 13.47 40.69 38.32 12.64 49.04 9 48.31 13.3 38.3938.61 11.92 49.47 10 45.77 13.48 40.74 38.23 12.01 49.76 11 51.16 14.7234.12 38.38 12.13 49.49 12 48.79 14.02 37.19 36.57 11.03 52.39

Referring to Table 1, in the case that the reflow process is notperformed after the hydrophobic layer HPL and the wall WL are formed,the content of fluorine (F) in the surface of the hydrophobic layer HPLis about 35at % to about 41at % and the content of oxygen (O) in thesurface ofthe hydrophobic layer HPL is about 11at % to about 15at %. Incomparison, in the case that the reflow process is performed after thehydrophobic layer HPL and the wall WL are formed, the content of F inthe surface of the hydrophobic layer HPL is about 49at % to about 53at %and the content of 0 in the surface of the hydrophobic layer HPL isabout 11at % to about 13at %. That is, when the reflow process isperformed after the hydrophobic layer HPL and the wall WL are formed,the content of F may be significantly increased and the relative contentof 0 to F may be significantly decreased. This means that when thereflow process is performed after the hydrophobic layer HPL and the wallWL are formed, the content off may be significantly increased in thesurface of the hydrophobic layer HPL and the hydrophobicity of thehydrophobic layer HPL may be significantly strengthened.

FIG. 6 is a plan view showing the electrowetting display device shown inFIG. 1 according to an exemplary embodiment of the present invention andFIG. 7 is a cross-sectional view taken along a line I-I shown in FIG. 6.FIGS. 6 and 7 show two pixels PXL adjacent to each other. In the presentexemplary embodiment, the range of each pixel PXL is an area between twowalls WL adjacent to each other and the first fluid FL1 is limited inthe pixel area PA.

Referring to FIGS. 6 and 7, the electrowetting display device includes,for example, a first substrate, a second substrate facing the firstsubstrate, and the first and second electrowetting layers EWL1 and EWL2are disposed between the first substrate and the second substrate.

The first substrate includes, for example, the first base substrate BS1,a plurality of gate lines GL disposed on the first base substrate BS1,and a plurality of data lines DL disposed on the first substrate BS1.The gate lines GL extend in, for example, a first direction and areformed on the first base substrate BS1. A first insulating layer INS1 isdisposed on the first base substrate BS1 on which the gate lines GLareformed. The first insulating layer INS1 includes, for example, a siliconnitride, a silicon oxide, a silicon oxynitride, a tantalum oxide, analuminum oxide, an alloy of carbon nitride or a mixture thereof. Thedata lines DL are formed, for example, on the first insulating layerINS1 and extend m a second direction crossmg the first direction. It isnoted that exemplary embodiments of the present invention are notlimited to the above positions for the gate lines GL and the data linesDL. For example, alternatively, the data lines DL may instead be formedon the first base substrate BS1 and extend in the first direction andthe gate lines GL may instead be formed on the first insulating layerINS1 and extend in the second direction crossing the first direction.

A thin film transistor TR is connected to a corresponding one of thegate lines GL and a corresponding one of the data lines DL. The thinfilm transistor TR includes, for example, a gate electrode GE, asemiconductor layer SM, a source electrode SE, and a drain electrode DE.

The gate electrode GE protrudes from the gate line GL. The gateelectrode GE includes, for example, a conductive material like metal,such as, for example, copper (Cu), molybdenum (Mo), aluminum (Al),tungsten (W), chromium (Cr), titanium (Ti), nickel (Ni), gold (Au),palladium (Pd), platinum (Pt), neodymium (Nd), zinc (Zn), cobalt (Co),any mixtures thereof and any alloys thereof. In addition, the gateelectrode GE may also be formed of other materials which include, forexample, a transparent conductive material such as an indium tin oxide(ITO), an indium zinc oxide (IZO) and an aluminum doped zinc oxide(AZO).

The semiconductor layer SM is disposed on the gate electrode GE and thefirst insulating layer INS1 is disposed between the semiconductor layerSM and the gate electrode GE. The first insulating layer INS1 isdisposed over the first base substrate BS1 to cover the gate line GLandthe gate electrode GE.

The semiconductor layer SM includes, for example, an active layerdisposed on the first insulating layer INS1 and an ohmic contact layerdisposed on the active layer. The active layer is disposed in an area inwhich the source electrode SE and the drain electrode DE are formed andan area corresponding to between the source electrode SE and the drainelectrode DE when viewed in a plan view. The active layer may include asilicon material such as, for example, amorphous silicon or polysilicon.Alternatively, the active layer may include, for example, an organicsemiconductor material. The ohmic contact layer is disposed between theactive layer and the source electrode SE and between the active layerand the drain electrode DE.

The ohmic contact layer may include, for example, amorphous silicondoped with n-type or p-type impurities. Alternatively, the ohmic contactlayer may include, for example, an oxide semiconductor layer. Forexample, the ohmic contact layer may include an oxide semiconductorlayer that includes one or more of the following elements: indium (In),gallium (Ga), zinc (Zn), tin (Sn), germanium (Ge), hafnium (Hf), andarsenide (As). For example, the ohmic contact layer may include, forexample, zinc oxide (ZnO), tin oxide (SnO₂), indium oxide (In₂O₃), zincstannate (Zn₂SnO₄), gallium oxide (Ga₂O₃), and hafnium oxide (HfO₂) inthe oxide semiconductor layer.

The source electrode SE is branched from the data line DL and partiallyoverlapped with the gate electrode GE when viewed in a plan view. Thedrain electrode DE is spaced apart from the source electrode SE andpartially overlapped with the gate electrode GE when viewed in a planview. The source electrode SE and the drain electrode DE include aconductive material, such as, for example, copper (Cu), molybdenum (Mo),aluminum (Al), tungsten (W), chromium (Cr), titanium (Ti), nickel (Ni),gold (Au), palladium (Pd), platinum (Pt), neodymium (Nd), zinc (Zn),cobalt (Co), any mixtures thereof and any alloys thereof. In addition,the source electrode SE and the drain electrode DE may also be formed ofother materials which include, for example, a transparent conductivematerial such as an indium tin oxide (ITO), an indium zinc oxide (IZO)and an aluminum doped zinc oxide (AZO).

In the present exemplary embodiment, the source electrode SE and thedrain electrode DE are overlapped with a portion of the semiconductorlayer SM in an area except the area between the source electrode SE andthe drain electrode DE. The area between the source electrode SE and thedrain electrode DE serves as a channel portion, and an upper surface ofthe active layer is exposed through the area between the source anddrain electrodes SE and DE. When the thin film transistor TR is turnedon, a current may flow between the source electrode SE and the drainelectrode DE through the channel portion.

A second insulating layer INS2 is disposed on the channel portion tocover and protect the channel portion. The second insulating layer INS2includes, for example, silicon nitride, silicon oxide, siliconoxynitride, tantalum oxide, aluminum oxide, an alloy of carbon nitrideor a mixture thereof. The second insulating layer INS2 covers a portionof the source electrode SE and a portion of the drain electrode DE.

The first electrode EL1 is connected to the drain electrode DE through acontact hole CH formed through the second insulating layer INS2 disposedbetween the first electrode EL1 and the drain electrode DE. A portion ofthe drain electrode DE is exposed through the contact hole CH and thefirst electrode EL1 is connected to the exposed portion of the drainelectrode DE through the contact hole CH.

In the present exemplary embodiment, when the electrowetting displaydevice is a transmission type electrowetting display device, the firstelectrode EL1 may include, for example, a transparent conductivematerial, such as indium tin oxide (ITO), indium zinc oxide (IZO), orindium tin zinc oxide (ITZO). In the case that the electrowettingdisplay device is a reflection type electrowetting display device, thefirst electrode EL1 may include a conductive material havingreflexibility, such as a metal material like, for example, aluminum. Inaddition, the first electrode EL1 may have, for example, a multi-layerstructure using the transparent conductive material and the conductivematerial having reflexibility. Further, when the electrowetting displaydevice is a transflective type electrowetting display device, the firstelectrode EL1 includes a reflective portion to reflect external lightand a transmissive portion to transmit external light. In this case, thefirst electrode EL1 may have a single-layer structure or a multi-layerstructure of the transparent conductive material and/or the conductivematerial having reflexibility.

The hydrophobic layer HPL is disposed on the first electrode EL1 tocover each pixel area PA.

In the present exemplary embodiment, a third insulating layer INS3 isdisposed between the first electrode EL1 and the hydrophobic layer HPL.The third insulating layer INS3 includes an insulating material, suchas, for example, silicon nitride (SiNx), silicon oxide (SiOx), siliconoxynitride, tantalum oxide, aluminum oxide, an alloy of carbon nitrideor a mixture thereof. The third insulating layer INS3 may have asingle-layer structure or a multi-layer structure.

The wall WL is disposed on the hydrophobic layer HPL of the firstsubstrate. The wall WL restricts the movement of the first fluid FL1 andis provided in each pixel area PA. A spacer (not shown) may be providedon the second substrate to correspond to at least a portion of the wallWL. The spacer maintains a distance between the first substrate and thesecond substrate.

As described above, the hydrophobic layer HPL includes, for example, amaterial having hydrophobicity, e.g., a compound of fluorine atoms. Thecompound may contain, for example, about 49at % of fluorine atoms ormore in its surface to allow the surface to have hydrophobicity. Thecompound may be, for example, a polymer compound represented by thefollowing chemical formulas, such as -CxFy-, CxFyHz-, -CxFyCzHp-,-CxFyO—, -CxFyN(H)—, etc., where each of x, y, x, p is an integer numberequal to or larger than 1), or an amorphous fluorine compound, such as,for example, copolymers of tetrafluoroethylene (TFE) and perfluro-2,2dimethyl 1, 3 dioxide (PDD), sold under the brand name TEFLON® AF 1600which is a registered trademark of the E.I. DuPont de Nemours andCompany Corporation, 101 West 10th St., Wilmington, Del. 19898).Alternatively, other low surface energy polymers such as, for example,parylene may be used to form the hydrophobic layer HPL.

For example, the hydrophobic layer HPL contains about 49at % of fluorineatoms in the surface thereof, and the contact angle of the water withrespect to the hydrophobic layer HPL is about 100° or more. Thehydrophobic layer HPL has a surface tension of, for example, about 16dyne/cm or more.

The hydrophobic layer HPL includes, for example, a planarization portionPLP substantially parallel to the upper surface of the first basesubstrate BS1 and the edge portion EDG disposed at the side portions ofthe planatization portion PLP and inclined with respect to the wall WL.The planarization portion PLP has, for example, a thickness of about 10nm or more to allow the hydrophobic layer HPL to have sufficienthydrophobicity when the hydrophobic layer HPL is formed. The surface ofthe edge portion EDG is bent upwardly as the edge portion EDG is closerto the wall WL. In other words, the end portion of the edge portion EDGmay protrude upward from the planarization portion PLP to directly makecontact with the wall WL. The contact angle of the hydrophobic layer HPLwith respect to the wall WL is, for example, smaller than the rightangle. The end portion of the edge portion EDG of the hydrophobic layerHPL is positioned, for example, at a height higher than a height of theend portion of the planarization portion PLP when viewed in across-sectional view. The height of the end portion of the edge portionEDG is, for example, lower than a height of the wall WL and larger thanabout 1/100 of the height of the wall WL. In addition, the height of theend portion of the edge portion EDG is, for example, smaller than about99/100 of the height of the wall WL.

The second electrode EL2 is disposed on the second base substrate BS2and applied with the common voltage. The second electrode EL2 includes,for example, the transparent conductive material, such as indium tinoxide, indium zinc oxide, or indium tin zinc oxide.

Although not shown in figures, either the first substrate or the secondsubstrate includes, for example, color filters (not shown) to realizered, green, and blue colors. In addition, for example, a black matrix(not shown) may be provided between the color filters to blockunnecessary light passing through between the color filters.

The first fluid FL1 and the second fluid FL2 are filled in between thefirst substrate and the second substrate. In FIG. 7, the first fluid FL1has been shown in the OFF-state. In addition, in FIG. 7, a meniscusbetween the first fluid FL1 and the second fluid FL2 has been shown in astraight line shape, but the meniscus may be slightly bent upward ordownward according to a filling process for the space and a type of thewall WL.

The electrowetting display device shown in FIGS. 6 and 7 may bemanufactured by forming the electronic device on the base substrate,forming the hydrophobic layer HPL on at least a portion of the basesubstrate, plasma-treating the hydrophobic layer HPL, forming the wallWL on the hydrophobic layer HPL, reflowing the hydrophobic layer HPL,and forming the first and second electrowetting layers EWL1 and EWL2.That is, the method of manufacturing the electrowetting display deviceaccording to the present exemplary embodiment is substantially same asor similar to the method of manufacturing the electrowetting displaydevice described with reference to FIGS. 3 and 4A to 4F.

For example, the method of manufacturing the electrowetting displaydevice according to the present exemplary embodiment includes preparingthe first base substrate BS1 and forming the switching device on thefirst base substrate BS1.

The gate electrode GE and the gate line GLare formed on the first basesubstrate BS1. The gate electrode GE and the gate line GLare formed by,for example, forming a conductive material, such as a metal material, onthe first base substrate BS1 and patterning the conductive materialusing a photolithography process.

Then, the first insulating layer INS1, an amorphous silicon layer, andan n+ amorphous silicon layer are sequentially deposited on the firstbase substrate BS1 on which the gate electrode GE and the gate line GLare formed. When the amorphous silicon layer and the n+ amorphoussilicon layer are selectively patterned by, for example, thephotolithography process, the semiconductor layer SM, which includes theactive layer and the ohmic contact layer that ohmic-contacts the sourceand drain electrodes SE and DE, is formed.

The conductive layer, such as a metal layer, is deposited on the firstbase substrate BS1 on which the semiconductor layer SM is formed, andthe conductive layer is patterned using, for example, a photolithographyprocess, thereby forming the data line DL, the source electrode SE, andthe drain electrode DE.

The semiconductor layer SM, the source electrode SE, and the drainelectrode DE may be formed by, for example, a two-time photolithographyprocess, but exemplary embodiments of the present invention are notlimited thereto or thereby. That is, the semiconductor layer SM, thesource electrode SE, and the drain electrode DE may be formed byone-time photolithography process using a slit mask or a half-tone mask.

After that, the second insulating layer INS2 is formed on the first basesubstrate BS1 on which the source electrode SE and the drain electrodeDE are formed. The second insulating layer INS2 is partially removed by,for example, a photolithography process to form the contact hole CHthrough which a portion of the drain electrode DE is exposed.

Then, when the transparent conductive material is deposited on the firstbase substrate BS1 and selectively patterned using a photolithographyprocess, the first electrode EL1 is formed to be electrically connectedto the drain electrode DE through the contact hole CH.

Next, the third insulating layer INS3 is formed on the first electrodeEL1 and the hydrophobic layer HPL is formed on the third insulatinglayer INS3.

The hydrophobic layer HPL is plasma-treated, and then the wall WL isformed on the plasma-treated hydrophobic layer HPL by using, forexample, a photolithography process.

Then, the plasma-treated hydrophobic layer HPL is, for example,reflowed.

The first and second electrowetting layers EWL1 and EWL2 are formedbetween the first substrate and the second substrate. The firstelectrowetting layer EWL1 may include, for example, the first fluid FL1and the second electrowetting layer EWL2 may include, for example, thesecond fluid FL2. In the present exemplary embodiment, the first fluidFL1 is formed in the display area defined by the wall WL.

FIG. 8 is a cross-sectional view showing a portion of an electrowettingdisplay device according to an exemplary embodiment of the presentinvention. The electrowetting display device includes a plurality ofpixels PXL, and one of the pixels PXL has been shown in FIG. 8. In FIG.8, a length of a side surface of the pixel PXL has been represented bytwo dotted lines.

Referring to FIG. 8, each pixel PXL includes, for example, a first basesubstrate BS1, a second base substrate BS2, a wall WL, a hydrophobiclayer HPL, and a first electrowetting layer EWL1 and a secondelectrowetting layer EWL2.

The first base substrate BS1 and the second base substrate BS2 face eachother and the first base substrate BS1 and the second base substrate BS2may be, for example, a transparent insulating substrate. Each of thefirst base substrate BS1 and the second base substrate BS2 is formed,for example, in a single body to be commonly shared by the pixels PXL orformed in plural numbers to be used as a portion of each pixel PXL.

The wall WL is disposed on the first base substrate BS 1 to define aspace surrounded by the first base substrate BS1 and the wall WL. Thespace may be, for example, a pixel area PA corresponding to each pixelPXL. Accordingly, the area of the pixel area PA is limited by the wallWL, and the area of the pixel area PA has been represented by dottedlines.

The first and second electrowetting layers EWL1 and EWL2 are provided inthe pixel area PA defined by the wall WL and the first substrate BS1 orthe second substrate BS2. The first electrowetting layer EWL1 mayinclude, for example, a first fluid FL1 and the second electrowettinglayer EWL2 may include, for example, a second fluid FL2. The first andsecond fluids FL1 and FL2 are, for example, immiscible with each other.The first fluid FL1 may include, for example, pigments or dyes todisplay the color. For example, in an embodiment, the first fluid FL mayinclude other dyes or pigments of primary colors such as red, green,cyan, magenta, blue, or yellow. Alternatively, in an embodiment, thefirst fluid FL may include a black dye or pigment.

The second fluid FL2 has, for example, an electrical conductivity or apolarity. For example, in an embodiment, the second fluid FL2 may be apolar liquid aqueous solution (Aq) such as, for example, water or a saltsolution such as, for example, a solution of sodium chloride orpotassium chloride in water. In the present exemplary embodiment, thesecond fluid FL2 includes, for example, potassium chloride or sodiumchloride solution (Aq) dissolved in a mixture of water and ethylalcohol. The second fluid FL2 may be, for example, transparent or have acolor. As an example, the second fluid FL2 may have a white color toabsorb or reflect light from the outside.

The hydrophobic layer HPL is disposed on the first base substrate B Siin the display area defined by the wall WL. The hydrophobic layer HPL isprovided in each pixel PXL to cover the pixel PXL and is separated fromthe hydrophobic layer HPL provided in an adjacent pixel PXL thereto bythe wall WL. That is, the hydrophobic layer HPL is not formed betweenthe wall WL and the first base substrate BS1 when viewed in across-sectional view.

Meanwhile, an insulating layer INS is disposed between the first basesubstrate BS1 and the hydrophobic layer HPL and between the first basesubstrate BS1 and the wall WL. The insulating layer INS may have, forexample, a multi-layer structure, e.g., a double-layer structure, or maybe omitted.

The hydrophobic layer HPL may have, for example, permeability orreflexibility. When the hydrophobic layer HPL has reflexibility, lightfrom the outside may be reflected by the hydrophobic layer HPL. Inaddition, the hydrophobic layer HPL may, for example, have a white coloror reflect a portion of the light corresponding to a specific wavelengthto have a specific color.

The hydrophobic layer HPL includes, for example, a planarization portionPLP substantially parallel to the upper surface of the first basesubstrate BS1 and an edge portion EDG disposed at side portions of theplanatization portion PLP and inclined with respect to the wall WL. Theedge portion EDG is disposed adjacent to the wall WL to directly makecontact with the wall WL.

Each pixel PXL includes, for example, an electronic device that appliesan electric field to the first and second electrowetting layers EWL1 andEWL2 to control the first and second electrowetting layers EWL1 andEWL2. The electronic device includes, for example, a first electrode EL1disposed on the first base substrate BS1, a switching device (not shown)connected to the first electrode EL1, and a second electrode EL2disposed on the second base substrate BS2. The first electrode EL1 isdisposed between the first base substrate BS1 and the hydrophobic layerHPL, and an insulating layer INS is disposed between the first basesubstrate BS1 and the first electrode EL1.

The first electrode EL1 is separated from the electrowetting layers EWL1and EWL2 by the hydrophobic layer HPL. The first electrode EL1 may beprovided in an arbitrary desired shape. The first electrode EL1 isapplied with a voltage signal by the switching device. The secondelectrode EL2 may be formed, for example, in a single body to cover allthe pixels PXL. Although not shown in figures, in the case that thesecond electrode EL2 is divided into a plurality of second electrodesEL2, which respectively correspond to the pixels PXL, the secondelectrodes EL2 may be electrically connected to each other by the secondfluid FL2.

In the present exemplary embodiment, the first electrode EL1 and thesecond electrode EL2 are respectively disposed on the first basesubstrate BS1 and the second base substrate BS2, but exemplaryembodiments of the present invention are not limited thereto or thereby.For instance, all the first and second electrodes EL1 and EL2 may bedisposed on the first base substrate BS1. In this case, the secondelectrode EL2 may be provided on at least one side portion of the firstelectrode EL1 and electrically insulated from the first electrode EL1.

The pixel PXL may be controlled by a voltage V applied between the firstelectrode EL1 and the second electrode EL2. The first electrode EL1disposed on the first base substrate BS1 is connected to the switchingdevice.

The movement of the first fluid FL1 may be limited in each pixel PXL bythe wall WL of the pixel PXL. The wall WL may have hydrophilicity topush out the first fluid FL1. In the present exemplary embodiment, thewall WL extends in a direction from the first base substrate BS1 to thesecond base substrate BS2. However, exemplary embodiments of the presentinvention are not limited to this positioning of the wall WL. Forexample, alternatively, in an embodiment, the wall WL may extend in adirection from the second base substrate BS2 to the first base substrateBS1.

The pixel PXL may be in an ON-state when the voltage difference, whichis not zero, is applied to the first electrode FL1 and the secondelectrode FL2. An electrostatic force caused by the voltage differencemay move the second fluid FL2 to the first electrode EL1, and thus thefirst fluid FL1 may be pushed out from at least a portion of thehydrophobic layer HPL to the wall WL surrounding the hydrophobic layerHPL. When the first fluid FL1 is completely pushed out, the first fluidFL1 may have a drop shape as shown by the dotted line. Accordingly, thehydrophobic layer HPL of the pixel PXL is exposed through the firstfluid FL1. When the voltage applied to the pixel PXL returns to aboutzero volts, the pixel PXL may return to an OFF-state, so the first fluidFL1 covers the hydrophobic layer HPL again. The first fluid FL1 may thusserve as an optical switch that is able to be electrically controlled ineach pixel PXL.

FIG. 9 is a flowchart showing a method of manufacturing anelectrowetting display device shown in FIG. 8 according to an exemplaryembodiment and FIGS. 10A to 10E are cross-sectional views showing amethod of manufacturing the electrowetting display device shown in FIG.1 according to an exemplary embodiment of the present invention.

For example, referring to FIG. 9, the electrowetting display device ismanufactured by forming the electronic device on the base substrate,forming the hydrophobic layer HPL on at least a portion of the basesubstrate, patterning the hydrophobic layer HPL, reflowing thehydrophobic layer HPL, and forming the first electrowetting layer EWL1and the second electrowetting layer EWL2.

Hereinafter, the method of manufacturing the electrowetting displaydevice will be described in detail with reference to FIGS. 9 and 10A to10F.

Referring to FIGS. 9 and 10A, the base substrate is prepared and theelectronic device is formed on the base substrate (S210).

The base substrate includes, for example, the first base substrate BS1and the second base substrate BS2. In FIG. 10A, only the first basesubstrate BS1 is shown and the second base substrate BS2 is omitted.

The electronic device includes the first electrode EL1, the secondelectrode EL2, and the switching device. For the convenience ofexplanation, only the first electrode EL1 of the electronic device isshown in FIG. 10A. The switching device is connected to the firstelectrode EL1 and includes, for example, a transistor, capacitor, and aconnection line. The electronic device is formed, for example, eitheronly on the first base substrate BS1 or on both of the first and secondbase substrates BS1 and BS2. In the present exemplary embodiment, thefirst electrode EL1 and the switching device are formed on the firstbase substrate BS1, and the second electrode EL2 is formed on the secondbase substrate BS2. The insulating layer INS is formed on the electronicdevice.

Referring to FIGS. 9 and 10B, the wall WL is formed on the insulatinglayer INS (S220). The wall WL may be formed of, for example, aphotosensitive organic material, such as a photoresist, or a heatcurable organic material. The wall WL may include, for example, an epoxycompound represented by the chemical formula 2.

In the case that the wall WL is formed of the photosensitive organicmaterial, the wall WL may be formed, for example, by a photolithographyprocess including exposure and development processes. For example, thephotosensitive organic material is patterned through thephotolithography process and cured through a baking process, therebyforming the wall WL with the photosensitive organic material.

Referring to FIGS. 9 and 10C, the hydrophobic layer HPL is formed on theinsulating layer INS on which the wall WL is formed (S230). Thehydrophobic layer HPL is formed to cover the upper surface of theinsulating layer INS and the wall WL.

The hydrophobic layer HPL is formed, for example, by using a compoundcontaining fluorine atoms. The compound of the hydrophobic layer HPL maybe, for example, a polymer compound, such as -CxFy-, CxFyHz-,-CxFyCzHp-, -CxFyO—, -CxFyN(H)—, etc., (where each of x, y, x, p is aninteger number equal to or larger than 1), or the amorphous fluorinecompound represented by the chemical formula 1, such as, for example,copolymers of tetrafluoroethylene (TFE) and perfluro-2,2 dimethyl 1, 3dioxide (PDD), sold under the brand name TEFLON® AF 1600 which is aregistered trademark of the E.I. DuPont de Nemours and CompanyCorporation, 101 West 10th St., Wilmington, Del. 19898). Alternatively,other low surface energy polymers such as, for example, parylene may beused to form the hydrophobic layer HPL.

Then, although not shown in figures, the hydrophobic layer HPL ispatterned to be remain only on the insulating layer INS (S240).Selectively, only the hydrophobic layer HPL formed on the upper surfaceof the wall WL is removed and the hydrophobic layer HPL formed on theside surface of the wall WL and on the insulating layer INS remains. Thepatterning of the hydrophobic layer HPL is performed by, for example, aphotolithography process using a photoresist and the remainingphotoresist is removed by a dry etch process. In addition, thepatterning is performed to expose a portion of the electronic device,e.g., a portion of the connection line, and thus external lines may beconnected to the electronic device.

The plasma-treatment performed to increase the adhesive property of thehydrophobic layer HPL is omitted. This is because the hydrophobic layerHPL is formed after the wall WL is formed.

Referring to FIGS. 9 and 10E, the hydrophobic layer HPL is, for example,reflowed (S250). Residues and hydrophilic functional groups (e.g., —OH,—CHO, —COOH, etc.) on the hydrophobic layer HPL are removed through thereflowing process, so that the hydrophobicity on the surface of thehydrophobic layer HPL may be increased. The residues and hydrophilicfunctional groups are generated in the process of forming the wall WL.The reflow process is performed, for example, by heating the hydrophobiclayer HPL at a temperature higher than a glass transition temperature Tgof the material for the hydrophobic layer HPL. The reflow temperature ofthe hydrophobic layer HPL is in a range of, for example, about 160° C.to about 280° C. When the hydrophobic layer HPL is formed of the organicmaterial represented by the chemical formula 1, the reflow process isperformed at the reflow temperature of, for example, about 160° C. ormore. For example, in an embodiment, the reflow process may be performedat the reflow temperature of about 220° C. for about one hour. In thereflow process, the atoms in the hydrophobic layer HPL may be rearrangedso as to allow an interfacial energy between the hydrophobic layer HPLand air to be minimized. Thus, the hydrophilic functional groups mayenter inside the hydrophobic layer HPL and hydrophobic functionalgroups, e.g., fluorine (F), may come up to the surface. As a result, thehydrophobicity of the hydrophobic layer HPL may be strengthened again.

In the reflow process, a creep phenomenon, in which the surface of theedge portion EDG slides upward along the wall WL as it is closer to thewall WL, may occur when the reflow temperature is equal to or higherthan the glass transition temperature and a surface tension differencebetween the hydrophobic layer HPL and the wall WL is equal to or higherthan gravity. In this case, the height of the end portion of the edgeportion EDG may be varied depending on, for example, the temperature,the process time, and the surface tension of the wall WL and thehydrophobic layer HPL of the reflow process. For example, when thehydrophobic layer HPL is represented by the chemical formula 1 and thewall WL is represented by the chemical formula 2, the surface tension ofthe hydrophobic layer HPL is about 17 dyne/cm and the surface tension ofthe wall WL is about 45 dyne/cm. The height of the end portion of theedge portion EDG may be varied depending on, for example, thetemperature, the process time, and the surface tension of the wall WLand the hydrophobic layer HPL of the reflow process.

Referring to FIGS. 9 and 10F, the first and second electrowetting layersEWL1 and EWL2 are formed between the first base substrate BS1 and thesecond base substrate BS2 (S260). The first electrowetting layer EWL1may include, for example, the first fluid FL1 and the secondelectrowetting layer EWL2 may include, for example, the second fluidFL2. In the present exemplary embodiment, the first fluid FL1 is formedin the display area defined by the wall WL.

The electrowetting display device manufactured by the above-mentionedmethod may reduce a non-closing defective when the electrowettingdisplay device is operated. According to the present exemplaryembodiment, the hydrophobicity of the hydrophobic layer HPL may bestrengthened by reflowing the hydrophobic layer HPL to which thehydrophilic functional groups are adsorbed. That is, during the reflowprocess, the atoms in the hydrophobic layer HPL may be rearranged so asto allow the interfacial energy between the hydrophobic layer HPL andair to be minimized. Thus, the hydrophilic functional groups may betransported inside the hydrophobic layer HPL and hydrophobic functionalgroups, e.g., fluorine (F), may be transported up to the surface of thehydrophobic layer HPL. As a result, the hydrophobicity of thehydrophobic layer HPL is strengthened and the non-closing defective maybe reduced.

FIG. 11 is a cross-sectional view showing an electrowetting displaydevice according to an exemplary embodiment of the present inventionshown in FIG. 8. The cross-sectional view of the electrowetting displaydevice shown in FIG. 11 corresponds to the cross-sectional view takenalong the line I-I′ of FIG. 6. In FIG. 11, the range of each pixel PXLis an area between two walls WL adjacent to each other and the firstfluid FL1 is limited in the pixel area PA.

The electrowetting display device shown in FIG. 11 is manufactured, forexample, by forming an electronic device on a base substrate, forming awall WL on the base substrate, forming a hydrophobic layer HPL on thebase substrate, reflowing the hydrophobic layer HPL, and forming a firstelectrowetting layer EWL1 and a second electrowetting layer EWL2. In thepresent exemplary embodiment, the process of forming the electronicdevice on the base substrate is substantially same as that of the methoddescribed with reference to FIG. 6. Thus, detailed descriptions of themethod of manufacturing the electrowetting display device according tothe present exemplary embodiment will be omitted.

Having described exemplary embodiments of the present invention, it isfurther noted that it is readily apparent to those of ordinary skill inthe art that various modifications may be made without departing fromthe spirit and scope of the invention which is defined by the metes andbounds of the appended claims.

What is claimed is:
 1. A method of manufacturing an electrowetting display device, comprising: forming a hydrophobic layer on a base substrate; forming one or more pixel walls on the hydrophobic layer, wherein the one or more pixel walls at least partially encloses a pixel area and partition the pixel area from adjacent pixel areas, and wherein the hydrophobic layer has a substantially constant thickness over a central portion of the pixel area and a varying thickness over a peripheral portion of the pixel area adjacent to the pixel wall; forming an electrowetting layer on the hydrophobic layer, the electrowetting layer including a first fluid and a second fluid, wherein the first fluid and the second fluid are immiscible with each other; and forming at least a portion of an electronic device on the base substrate, wherein the electronic device is configured to apply an electric field to the electrowetting layer.
 2. The method of claim 1, wherein forming the hydrophobic layer comprises: forming a first hydrophobic layer on the base substrate; and reflowing the first hydrophobic layer at a temperature higher than a glass transition temperature of the first hydrophobic layer to form the hydrophobic layer, wherein the hydrophobic layer has a hydrophobicity greater than the hydrophobicity of the first hydrophobic layer.
 3. The method of claim 1, wherein the hydrophobic layer is a permeable parylene layer.
 4. The method of claim 1, wherein the electronic device comprises: a switching device disposed on the base substrate; a first electrode connected to the switching device; and a second electrode spaced apart from the first electrode by at least the electrowetting layer.
 5. A method of manufacturing an electrowetting display device, comprising: forming an electrode on a substrate; forming an electronic switching device on the substrate; at least partially covering the electrode and the electronic switching device with an insulating layer; forming at least one wall on the insulating layer to partition a pixel area; forming a first hydrophobic layer on the at least one wall and the insulating layer, the first hydrophobic layer having a first hydrophobicity; patterning the first hydrophobic layer to remove at least a portion of the first hydrophobic layer from a top of the at least one wall; and reflowing the first hydrophobic layer at a reflow temperature to form a second hydrophobic layer, the second hydrophobic layer having a second hydrophobicity that is greater than the first hydrophobicity.
 6. The method of claim 1, wherein the reflowing is performed by heating the first hydrophobic layer to the reflow temperature in a range of about 160° C. to about 260° C.
 7. The method of claim 1, wherein the reflowing further comprises reflowing the first hydrophobic layer at the reflow temperature higher than a glass transition temperature of the first hydrophobic layer to enable creep to form an edge portion of the second hydrophobic layer, wherein a thickness of the edge portion of the second hydrophobic layer increases as a distance to the wall decreases.
 8. The method of claim 1, wherein forming the wall comprises: patterning a photosensitive organic material that includes an epoxy compound by a photolithography process; and curing the patterned photosensitive organic material by a baking process to form the wall.
 9. The method of claim 1, wherein a surface of the second hydrophobic layer comprises at least about 49 atomic percent (at %) of fluorine atoms.
 10. The method of claim 1, wherein patterning the first hydrophobic layer to remove the first hydrophobic layer from at least a top of the wall further comprises leaving portions of the first hydrophobic layer on sides of the wall.
 11. A method of manufacturing an electrowetting display device, comprising: forming a first hydrophobic layer having a first hydrophobicity on a base substrate; forming a wall on the base substrate to partition a pixel area; reflowing the first hydrophobic layer at a temperature higher than a glass transition temperature of the first hydrophobic layer to form a second hydrophobic layer having a second hydrophobicity greater than the first hydrophobicity; and forming a fluid layer in the pixel area.
 12. The method of claim 11, wherein forming the wall comprises: patterning a photosensitive organic material that includes an epoxy compound by a photolithography process; and curing the patterned photosensitive organic material by a baking process to form the wall.
 13. The method of claim 12, wherein the second hydrophobic layer is disposed on the base substrate, and wherein the second hydrophobic layer comprises at least about 49 atomic percent (at %) of fluorine atoms in a surface thereof.
 14. The method of claim 13, wherein the second hydrophobic layer includes an amorphous fluorine compound comprising at least one of -CxFy-, CxFyHz-, -CxFyCzHp-, -CxFyO—, or -CxFyN(H)—, and wherein each of x, y, x, p is an integer number which is no less than
 1. 15. The method of claim 11, further comprising: forming an opposite substrate facing the base substrate; and forming an electronic device that controls the electrowetting layer, wherein a first portion of the electronic device is formed on the base substrate and a second portion of the electronic device is formed on the opposite substrate.
 16. The method of claim 15, wherein the first portion of the electronic device includes a switching device on the base substrate and a first electrode connected to the switching device.
 17. The method of claim 15, wherein the second portion of the electronic device includes a second electrode is formed on the opposite substrate.
 18. The method of claim 11, wherein the forming of the first hydrophobic layer is performed prior to the forming of the wall.
 19. The method of claim 18, further comprising plasma-treating the first hydrophobic layer prior to the forming of the wall.
 20. The method of claim 11, wherein the forming of the first hydrophobic layer is performed between the forming of the wall and the forming of the electrowetting layer. 